In recent years, a device control system has been developed to display graphics and icons comprising data and texts for display on a TV screen so as to indicate the functions of the device, and to control the device by selectively controlling the graphics or icons with a remote controller of the TV. Further, a network control system has been developed to connect digital devices such as a digital VTR by using the IEEE 1394-1995 standard, and to exchange video/audio data between the devices.
Hereinafter, such a network control system will be described briefly.
An AVC system utilizing the conventional network control system is constructed such that each AV device is connected with another AV device by a serial bus which can periodically give a chance of equal communication in a bi-directional packet communication system, without changing the connection of each AV device. A digital interface based on the IEEE 1394 standard is used, for example, as the serial bus.
Each AV device stores its own data for display. The AV device transmits the display data to a controller in response to a request from the controller having a graphic display function, such as a television receiver.
Upon receipt of the display data, the controller displays the display data. When the controller reads the display data, the controller issues a read command to the AV device, and reads desired data as a response from the AV device. When the desired data is larger than the buffer amount in each AV device, the controller repeatedly issues the read command so as to obtain the remaining data.
Further, the controller has the function of inquiring about data that is required for the display of the connected AV device, and the function of controlling the display screen based on the display data that is transmitted from the AV device.
Each AV device has a recording medium which stores the display data, and the function of selecting appropriate display data in response to the inquiry about the display data from the controller.
In the network control system for the AVC system so constructed, the display data is stored in each device (AV device) and the graphics of each device (AV device) are displayed on the screen of the controller by outputting the display data in response to the display request from the controller (television receiver).
Japanese Published Patent Application No. Hei. 9-149325 discloses an example of a conventional network control system, and Japanese Published Patent Application No. Hei. 10-290238 discloses an example of a mass data transmission method.
In the above-described construction, however, the controller must repeatedly issue the command according to the buffer amount of the AV device when the AV device transmits mass data and, therefore, overhead increases and the transmission efficiency of the transmission line is degraded. As the result, the data transmission time is increased.
The present invention is made to solve the above-described problems, and an object of the present invention is to provide a network control system which can transmit mass data such as icon data efficiently, rapidly, and reliably, and which can decide what is transmitted from the target even when the target spontaneously transmits it. Further, another object of the present invention is to provide a controller, a target, and a consumer for the network control system.